The present invention pertains generally to methods for constructing infrared detectors and more particularly to methods for constructing epitaxial film, metal contact infrared detectors (including Schottky barrier detectors) sensitive to radiation in the 8- 14 microns atmospheric window of the electromagnetic spectrum.
Various methods exist for constructing semiconductor junctions-detectors which are responsive to electromagnetic radiation. A common method uses bulk material and a number of complex photolithographic steps to form junctions which run parallel to the semiconductor surface. Structures formed by this method are constructed such that they must be mechanically self-supporting. Their resulting relative massiveness makes it difficult to obtain efficient radiation exposure of their junctions.
Epitaxial films have been used to alleviate some of the problems posed by bulk detectors. Epitaxial films are grown in single crystalline structures on crystalline substrates, such as barium fluoride, by various evaporation techniques. Compared with etched bulk materials, these epitaxial films provide relatively thin semiconductor layers. The films, in addition, solve the radiation exposure or quantum efficiency problems, by allowing radiation to enter the semiconductor film through a non-absorbing substrate, whereas in bulk material the radiation enters through a thick layer of semiconductor material. Epitaxial films have, of course, been grown by various techniques. However, the quasiequilibrium technique (cool method) for growing films as disclosed in an article entitled "Thick Epitaxial Films of Pb.sub.1.sub.-x Sn.sub.x Te" in The Journal of Vacuum Science and Technology, Vol. 9, No. 1, pp. 226-230, by R. F. Bis, J. R. Dixon and J. R. Lowney has been proven to be a superior method for growing epitaxial films. Epitaxial films formed by this technique adhere firmly to the substrate facilitating handling and creating a generally more durable device. In addition, the electrical properties of the films can be controlled effectively during growth, making costly and time consuming post growth treatments largely unnecessary.
Schottky barrier devices have been developed to detect infrared radiation which have utilized the conventional complex and time consuming evaporation techniques for growing epitaxial films. The further step of formation of Schottky barriers on films grown by the conventional techniques certainly has not proved to be a simplier or less costly procedure.
Schottky barrier detectors have also been constructed with epitaxial film layers of Pb.sub.1.sub.-x Sn.sub.x Te formed by techniques similar to quasiequilibrium technique but have relied on electroplating rather than evaporation methods to form the detector metal-semiconductor junction. However, electroplating requires breaking of the vacuum after depositing the epitaxial film and exposing the surface of the film to potentially contaminating gas-ambients. Exposing the semiconductor to ambient gases after growth, runs the risk of degrading the electro-optical properties of the metal semiconductor contact to be formed, hence degrading the performance of the device.